1. Field of the Invention
The present disclosure generally relates to a protective layer setting unit for applying a protective agent to an image carrying member used for an image forming apparatus employing electrophotography, and a process cartridge having the protective layer setting unit.
2. Description of the Background Art
Typically, an image forming apparatus using electrophotography produces an image by sequentially conducting a series of processes such as a charging process, an exposure process, a developing process, and a transfer process to a photoconductor such as an OPC (organic photoconductor). After conducting the transfer process, by-products generated by discharging during the charging process or toner particles remaining on the photoconductor are removed by a cleaning process. The cleaning process can be conducted by using a cleaning blade, such as a rubber blade, which has a relatively simple and inexpensive structure but which cleans well.
However, a cleaning blade has a short lifetime and can itself reduce the useful life of the photoconductor because the cleaning blade is pressed against the photoconductor to remove residual materials remaining on the photoconductor. More specifically, frictional pressure between the cleaning blade and the photoconductor causes abrasion on the rubber blade and a surface layer of the photoconductor.
Further, small-sized toner particles, used for coping with demand for higher quality images, may not be effectively trapped by the cleaning blade, referred to as “passing of toner” or “toner passing.” Toner passing is more likely to occur by insufficient dimensional or assembly precision of the cleaning blade or when the cleaning blade vibrates unfavorably due to an external shock or the like. If toner passing occurs, higher quality images may not be produced.
Accordingly, to enhance the lifetime of the photoconductor and to produce higher quality images over time, frictional pressure on the photoconductor or cleaning blade needs to be reduced, and the cleaning performance of the photoconductor needs to be enhanced, by which degradation of the photoconductor or cleaning blade can be reduced and “toner passing” can be reduced.
In view of such frictional pressure reduction and cleaning performance enhancement, in general, a lubricant is applied to the photoconductor to form a lubricant layer on the photoconductor using the cleaning blade. The lubricant layer can protect the surface of the photoconductor from an effect of frictional pressure caused by the cleaning blade pressing against the photoconductor, which abrades the photoconductor, or from a discharge energy effect during a charging process, which degrades the photoconductor. Further, the photoconductor having a lubricant layer can enhance lubricating performance of the photoconductor surface, by which an unfavorable vibration of cleaning blade can be reduced, and thereby the toner passing amount can be reduced.
Because lubricating and protection performance of a lubricant may be affected by an amount of lubricant applied on the photoconductor, the application amount of the lubricant may need to be controlled to a given level. If the application amount of lubricant is too small, the aforementioned photoconductor abrasion by frictional pressure, photoconductor degradation by charging process, and toner passing may not be effectively reduced. Accordingly, the state of the lubricant application on the photoconductor, such as application amount, needs to be evaluated.
In general, a metallic soap such as zinc stearate is used as the lubricant. When zinc stearate is used as the lubricant, the amount of zinc stearate applied to a photoconductor is analyzed using XPS (X-ray photoelectron spectroscopy), in which the amount of zinc element as a percentage of all elements on the surface of photoconductor is measured.
In XPS analysis, elements other than hydrogen existing in a top and a sub-surface of a sample can be detected. When an OPC (organic photoconductor) coated with zinc stearate is analyzed using XPS, an element amount profile detected by XPS varies depending on a coating amount or coating ratio of zinc stearate. For example, when no zinc stearate is applied to the OPC, the element amount profile shows an element distribution of the OPC itself, whereas when zinc stearate is applied to the OPC, the element amount profile shows a mixture of the element distribution of the OPC and the element distribution of the zinc stearate. If the zinc stearate is applied to the entire surface of the OPC (i.e., OPC is coated with zinc stearate 100%), the element amount profile only shows the element distribution of the zinc stearate, and therefore an upper limit of zinc amount or ratio on the OPC becomes a zinc amount or ratio of the zinc stearate. Accordingly, when zinc stearate, which has a chemical composition of C36H70O4Zn, coats the entire surface of the photoconductor, theoretically the ratio of zinc to all elements should be 2.44%, which is computed from the ratio of elements in zinc stearate (C36H70O4Zn) excluding hydrogen.
Recently, a charging process for electrophotography has been employing an AC charging using a charge roller, in which an alternating current voltage is superimposed on the direct current voltage. Such AC charging can charge a photoconductor more uniformly, can reduce generation of oxidizing gas, such as ozone and nitrogen oxide (NOx), and can contribute to size reduction of an image forming apparatus, for example. However, a photoconductor may be increasingly degraded because a discharge of positive and negative voltages repeatedly occurs between a charging device and the photoconductor with a frequency of the applied alternating current voltage, such as several hundred to several thousand times per second. Such degradation of the photoconductor can be reduced by applying a lubricant, such as metallic soap, on the photoconductor because the lubricant can absorb discharge energy of the AC charging so as to prevent the discharge energy effect to the photoconductor.
The lubricant (e.g., metallic soap) may be decomposed by the AC charging. However, the metallic soap is not decomposed completely, but may be decomposed to a lower molecular weight fatty acid, and a friction pressure between the photoconductor and a cleaning blade may increase as the lubricant is decomposed. Such fatty acid and toner may be adhered on the photoconductor as a film, by which image resolution is degraded, the photoconductor is abraded, and uneven image concentration occurs.
In light of this phenomenon, a greater amount of metallic soap may be applied on the photoconductor so as to effectively coat a surface of the photoconductor with metallic soap even if some fatty acid may be generated. However, only some of the metallic soap may actually adhere on the photoconductor even if the photoconductor is supplied with a greater amount of metallic soap, and most of the metallic soap applied on the photoconductor may be transferred with toner, or removed with waste toner, for example. Accordingly, the metallic soap may be consumed rapidly, and the metallic soap may need to be replaced with new metallic soap in a time period, which may be shorter than a lifetime of the photoconductor.
In view of such drawbacks, instead of using metallic soap, higher alcohols having a greater carbon number, such as from 20 to 70, are used as a main component of a lubricant (or protective agent) in one conventional art. When the lubricant is applied to a photoconductor, higher alcohol may accumulate on a leading edge of a cleaning blade as indefinite-shaped particles, and the lubricant has surface wet-ability with the surface of photoconductor, by which the lubricant can be used for a long period of time.
However, if the higher alcohol is used as lubricant, one molecule of higher alcohol may coat a relatively larger area on the photoconductor, and thereby density of higher alcohol molecules absorbed on the photoconductor per unit area may become smaller (i.e., smaller molecular weight per unit area), which is not preferable from a viewpoint of reducing the electrical stress of the AC charging to the photoconductor.
Another art proposes using powder of an alkylene bis alkyl acid amide compound as a lubrication component to supply powder in the surface boundaries between a photoconductor (or image carrying member) and a cleaning blade in a contacting condition with the photoconductor so as to provide smooth lubrication effect on the surface of the photoconductor for a long period. However, if a lubricant having nitrogen atom is used, the lubricant itself may generate decomposition products having ion-dissociative property, such as nitrogen oxide and a compound having ammonium when the lubricant is subjected to the electrical stress of AC charging. Such products then intrude into a lubrication layer, thereby reducing resistance of the lubrication layer under a high-humidity condition and may result in occurrences of grainy images.
Recently, it is known that a protective agent having paraffin as a main component can protect a photoconductor from the electrical stress of AC charging, can reduce a frictional pressure between the photoconductor and a cleaning blade, and can remove toner remaining on the photoconductor, for example. Further, the protective agent having paraffin may not generate fatty acid so much even if the protective agent is oxidized by the electrical stress of AC charging, which is preferable for reducing fluctuation or variation of the frictional pressure between the photoconductor and the cleaning blade.
However, when image forming operations are repeated using a protective agent having paraffin, abnormal images, such as streak image, were produced in some cases, wherein such abnormal images may be caused by abrasion of the photoconductor and the cleaning blade. Based on research, the probability of such abnormal images varies among product lots of protective layer setting units. Research was further conducted for photoconductors, which exhibited or did not exhibit the abnormal images, to find that the abnormal images occurred on an area where a layer thickness of the photoconductor was relatively thinner or an area where toner was attracted with a greater amount on the photoconductor. However, the root causes of such abnormal images are not known yet.
As noted above, paraffin can be effectively used as a protective agent instead of metallic soap. However, when a protective agent, such as paraffin, not containing metal component is subjected to OPC, XPS or XRF analysis, one only observes peak values for carbon (C) and oxygen (O), and therefore the amount of protective agent applied to the photoconductor may not be effectively evaluated. Further, ICP spectroscopic analysis may not be suitable for effectively evaluating the amount of protective agent, not containing metal component, applied to the photoconductor because the ICP spectroscopic analysis is also used for detecting a protective agent (e.g., metallic soap) having metal component. If the amount of protective agent on a photoconductor cannot be effectively evaluated, a photoconductor having an insufficient amount of protective agent may be assembled in a process cartridge or an image forming apparatus, and the photoconductor can cause image quality degradation.
As such, a conventional analysis method may not be suitable for detecting the amount of a protective agent, such as paraffin, that does not include a metal component. In view of such background, a method of effectively evaluating a surface condition of a photoconductor coated with a protective agent not including metal component is desired, as well as a protective layer setting unit configured to apply such a protective agent within the range of efficacy required.